(i) Three point test cross.
(ii)

If we analyse the loci of two alleles at a time, starting with AB, since AB and ab are parental genotypes, the recombination will be Ab/aB.
The recombinant frequency for these two alleles can be calculated as follows.
\(RF = \frac{Total\ no.\ of \ recombination}{Total\ no.\ of\ progenies}\times100\)
\(\mathrm{RF}=\frac{114+5+4+116}{1200} \times 100 \)
\(\mathrm{RF}=\frac{239}{1200}=19.91 \)
For A and C loci, the recombinants are Ac / aC - RF will be as follows.
\(\mathrm{RF}=\frac{114+134+116+128}{1200} \times 100 \)
\(\mathrm{RF}=\frac{482}{1200}=40.1 \)
For B and C loci, the recombinants are Bc / bC- RF will be as follows.
\(R F=\frac{124+5+4+128}{1200} \times 100 \)
\(R F=\frac{261}{1200}=21.75 \)
All the loci are linked, because all the RF value is less than 50%. In this A - and C loci show highest RF value, they must be farthest apart. Therefore B locis must lie in between them.
The order of genes should be abc. A genetic map can be drawn as follows.
(iii)
 

(i) Incomplete linkage

Rano : 1:2:1

(i) Complete Linkage
(ii)
 
(iii) Observed ratio 1:1 

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Sometimes, the chromosome number of somatic cells changed due to addition or elimination of individual chromosome or basic set of chromosomes. This condition in known as ploidy.

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A sudden change in the genetic material of an organisms is called mutation. The term mutation was introduced by Hugo de Vries.

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